BRUCELLOSIS
Brucellosis is primarily a disease of animals with a predilection for organs rich in
erythritol (breast, uterus, placenta, epididymis). The organism localizes in these animal organs
and causes infertility, sterility, mastitis, abortion, or carrier state in non-human animals.
Brucellosis is common where significant disease if found among the domestic animal
population. The Centers for Disease Control listed as high risk for potential risk of exposure to
Brucella the following areas; Mediterranean Basin (Portugal, Spain, Southern France, Italy,
Greece, Turkey, and North Africa), South and Central America, Eastern Europe, Asia, Africa,
the Caribbean, and the Middle East. Unpasteurized cheeses, from these areas are a particular risk
for tourists. Brucellosis is often referred to as undulant fever, Malta fever, and Mediterranean
remittent fever.
The bacteria can penetrate intact skin. Therefore, two types of patient populations are
seen. Humans in close contact with infected animals (slaughterhouse workers, veterinarians,
farmers, dairy workers) are at risk of developing brucellosis and individuals who ingest
unpasteurized dairy products contaminated with Brucella.
Four different species of Brucella infect humans and each bacterial species is animal host
specific: B. abortus (cattle), B. suis (swine), B. melitensis (goats/sheep) and B. canis (dogs).
Morphology and physiology:
Brucella are poorly staining Gram-negative, small coccobacilli that grows slowly
(fastidious) on 5% sheep blood agar, or chocolate agar. Isolates typically do not grow on
MacConkey agar or Eosin methylene blue (EMB) agar. Brucella appears mostly as single cells
and look like â&#x20AC;&#x153;fine sandâ&#x20AC;?. These organisms are nonhemolytic and nonmotile. Brucella species
are strict aerobes, except for some strains of B. abortus which require 5 % CO2 on primary
isolation. They are catalase, oxidase and urease positive. The urease test is specifically useful
for characterization of the Brucella. B. suis and some B. melitensis strains produce a rapid
1

reaction that can be observed within 5 min of inoculation on a Christensenâ&#x20AC;&#x2122;s urea slant. The
other Brucella species produce a positive reaction after overnight incubation.
Public Health Aspects:
Animal Sources:
Four species of Brucella cause brucellosis when transmitted to humans.
1. B. abortus primarily from cattle
2. B. melitenus from sheep, goats and camels
3. B. suis from pigs
4. B. canis from dogs
Patient Populations:
2 distinct populations
1. Individuals who work with or are exposed to unvaccinated animals. This group is
exposed via direct skin contact and inhalation. Farmers, veterinarians, slaughterhouse
workers, hunters and laboratory workers contract brucellosis in this way.
a. B. abortus
b. B. suis
2. Individuals who ingest unpasteurized dairy product are exposed in this way. Tourists and
individuals from areas with unvaccinated animals develop brucellosis via this route.
a. B. melitensis
Epidemiology:
There are 100-200 cases of brucellosis seen in the US, although the worldwide incidence
is significantly larger. B. suis is endemic in the feral swine population in 35 states including
South Carolina.
Symptoms:
In the animal host brucellosis may be asymptomatic or cause only a mild disease.
Brucellosis in animals may also lead to sterility, abortions and a carrier state in the non-human
animal.
In humans symptoms can appear up to 2 months after exposure. During the acute phase
(<8 weeks from illness onset) the patient presents with nonspecific and "flu-like" symptoms.
These include fever, sweats, malaise, anorexia, headache, myalgia, back pain, chills, fatigue,
weight loss, arthralgias, and non-productive cough. The fever may be intermittent fever
(undulant fever). As the disease advances into the undulant form or advanced disease (<1
year from illness onset) symptoms include undulant fevers, arthritis, and epididymo-orchitis in
males. Chronic disease (>1 year from onset) can mimic miliary tuberculosis with suppurative
lesions in the liver, spleen, and bone. The patient may have recurrent fevers, arthritis,
depression, and chronic fatigue syndrome. Brucellosis may lead to granulomatous hepatitis,
peripheral arthritis, leucopenia, thrombocytopenia, meningitis, and endocarditis.
The clinical spectrum of disease is dependent on the infecting organism. The following
table is a summary.

2

Organism
B. abortus

Animal
reservoir
Cattle

B. canis

Dogs

B. suis

Swine

B. melitensis

goats/sheep

Human disease

Complications

mild suppurative febrile
infection
mild suppurative febrile
infection
Prolonged disease which may
lead to the formation of
destructive lesions of the
lymphoreticular organs and
kidney
Severe and recurring disease

Rare
Rare

high incidence of serious
complications

Pathogenesis:
In the host, Brucella survives as facultative intracellular pathogens within the
reticuloendothelial system. Following penetration of the mucosal epithelium
(ingestion/inhalation routes, abraded skin, or the conjunctiva) the bacteria are transported via
macrophages to the regional lymph, leading to acute lymphadenitis. Brucella inhibits the
myeloperoxidase-H2O2-halide antibacterial systems in neutrophils hampering degranulation. In
the macrophage Brucella inhibits phagosome-lysosome fusion allowing the bacteria to survive
and multiply. The systemic spread and multiplication of Brucella in lymph nodes, spleen, liver,
bone marrow, mammary glands, and sex organs occurs via macrophages. Once distributed to
other organs the bacteria induce the formation of granulomas and/or micro abscesses. The ability
of Brucella to survival in macrophages is responsible for the establishment of chronic infections.
Brucella species do not produce exotoxins.
Diagnosis:
Diagnosis is based on presence of clinical presentation (undulant fever, myalgia,
arthralgias) and the history of exposure (contact with animals or consumption of unprocessed
material from infected animals). Definitive diagnosis can be made by culture (culture positive
blood, bone, tissue or abscess fluid). The (fastidious) organisms grow very slowly. Serological
testing such a serum agglutination test (SAT) can be a valuable diagnostic tool. A four-fold rise
in the SAT titer between the acute and convalescent phase sample is indicative of brucellosis.
Prevention and treatment:
Prolonged treatment with tetracycline, doxycycline, or trimethoprimsulfamethoxazole in
combination and rifampin or gentamicin for 6 weeks is used to prevent reoccurring infections.
Control measures include animal vaccination and avoidance of infected material (e.g.,
unpasteurized dairy products).

TULAREMIA
Francisella tularensis is the causative agent of tularemia. Its primary reservoirs are
rabbits, deer, and rodents; however F. tularensis has been isolated from over 100 species of
wild animals. Humans commonly acquires tularemia via the insect bites (ticks primarily, but
3

also deer flies, mites, black flies, or mosquitoes) or by handling infected animal tissues,
inhalation of aerosols or ingestion of contaminated food and water.
F. tularensis is a gram negative coccobacillus and two major biotypes of F. tularensis
are seen. Biotype A (F. tularensis subsp. tularensis) is found only in North America and is
more virulent, Biotype B (F. tularensis subsp. holarctica) is found in Europe and Asia and is
less virulent. Human disease (rabbit or deer fly fever) is characterized by a focal ulcer at the site
of entry of the organisms and enlargement of the regional lymph nodes. It takes as few as 10-50
organisms to infect via the aerosol or intradermal route.
Morphology and physiology:
F. tularensis is a small, Gram-negative, nonmotile, encapsulated, pleomorphic
coccobacillus (short rod). The organism grows poorly on most lab media and requires media
containing glucose and cysteine, for isolation. F. tularensis will grow on chocolate agar, and
buffered charcoal yeast extract agar. Organisms do not grow on MacConkey or eosin-methylene
blue (EMB) agars.
The organism is aerobic and slow growing so prolonged incubation times are needed (48
hours minimum, hold for 5 days) at 35-370 C. Colony morphology at 24 hours is too small to be
seen. At 48 hours, colonies are 1 to 2 mm in diameter, white to gray to bluish-gray, opaque, flat,
and smooth with an entire edge and shiny surface.
Biochemical screening tests:
•
•
•
•
•
•

Public Health-Modes of Infection:
In the United States, biting arthropods such as ticks and biting flies are the most
important vectors.
Outbreaks in the United States have been associated with infected rabbits, muscrats,
prairie dogs sold as pets, and the use of lawnmowers and brush cutters. Tularemia has been
reported in individuals who sustained bites from hamsters and cats. Occupations at increased risk
for transmission of tularemia include laboratory workers, landscapers, farmers, veterinarians,
hunters, trappers, cooks, and meat handlers. Naturally occurring cares are seen during the
summer months when people are exposed to ticks and biting flies and during hunting season.
Epidemiology and symptoms:
Tularemia occurs routinely in all 50 of the United States (~100 cases per year) primarily
in the south central (Arkansas, Missouri and Oklahoma) and western states. As few as10-50
bacilli will cause disease in humans if inhaled or introduced intradermally, whereas a very large
8
inoculum (~10 organisms) is required for the oral route of infection.
4

The incubation period is 3-10 days with a range of 1-14 days. The clinical manifestations
of tularemia can be divided into 5 groups: Ulceroglandular form is most common (45-85%) in
which a painful ulcerating papule which has a necrotic center and raised periphery develops at
the site of infection, glandular (without ulcer), typhoidal, pneumonic, oculoglandular, and
oropharyngeal/ gastrointestinal. Ingestion of infected meat or water can result in
oropharyngeal or gastrointestinal tularemia
The main difference between these groupings is the involvement of the skin/mucous
membranes and associated lymphadenopathy. In ulceroglandular tularemia a local painful
cutaneous lesion forms at site of inoculation and the papule ulcerates within a few days.
Ulceration is accompanied with fever, tender regional lymphadenopathy, and flu-like symptoms
(chills, myalgias, malaise, arthralgias, headache, and anorexia).
Typhoidal tularemia (sepsis) is distinguished by clinical findings of a high fever,
splenomegaly, and hepatomegaly Patients who have typhoidal form of tularemia also commonly
have associated gastrointestinal and pulmonary symptoms as well as the typical flu-like
symptoms. Typhoidal tularemia can result from pulmonary or gastrointestinal tularemia.
Pneumonia is a complication in 30% of patients with ulceroglandular tularemia and 80%
of patients with typhoidal tularemia. Pneumonic tularemia results from exposure to aerosolized
particles of F. tularensis or from hematogenous spread. Patients often present with communityacquired atypical pneumonia nonresponsive to conventional antibiotic therapy
Pathogenesis:
F. tularensis is a facultative intracellular parasite that multiplies predominately in
macrophages. The capsule of the organism renders it resistant to killing by complement. Uptake
by macrophages involves serum complement and receptors for C3. Once inside the macrophage
F. tularensis arrests maturation of the phagosome (LPS-O antigen is important for intracellular
survival) and enters into the cytosol where it multiplies to high levels and triggers apoptosis of
the macrophage which results in the release of the bacteria into surrounding tissue. Little is
known about specific pathogenesis factors.
Diagnosis:
F. tularensis is difficult to visualize in direct smears by Gram stain, but direct
fluorescent-antibody (DFA) staining will improve visualization. Lymph node aspirates and
sputum (pneumonic) are cultured on chocolate agar or buffered charcoal yeast extract agar
(BCYE). Blood cultures are often negative (7days incubation or longer). The organism grows
very slowly and hence must be incubated for several days. Serum antibody testing is the most
common for identification of F. tularensis. Culture of F. tularensis is not generally done in the
clinical laboratory and requires utilization of a biosafety cabinet for processing of samples.
Prevention and treatment:
Streptomycin is the drug of choice, gentamycin is an alternative. A live attenuated
vaccine is available but it is not completely effective. One must avoid handling infected animals,
watch out for ticks and utilize clean water supplies.

5

Yersinia
Three strain of Yersinia can cause human disease, Y. pestis, Y. enterocolitica and Y.
pseudotuberculosis. Y. enterocolitica and Y. pseudotuberculosis cause gastroenteritis, Y. pestis
causes plague.
Morphology and physiology:
Yersinia pestis is a pleomorphic, Gram-negative, bipolar staining, facultatively anaerobic,
bacillus. Optimal temperature for growth is 28째C. It is a facultative intracellular parasite. This
organism grows well on standard laboratory media (sheep blood agar). It is non-hemolytic, nonmotile, oxidase and urease negative.
Epidemiology, transmission and symptoms:
The three documented pandemics of plague (Black Death) have been responsible for the
death of hundreds of millions of people. Today, sporadic infections still occur. In the U.S.,
animal (sylvatic) plague occurs in a number of western states, usually in small rodents, and
carnivores that feed on these rodents. Human cases (Urban plague) occur occasionally,
particularly in the southwestern US. This is generally spread through rats in the urban
environment.
Humans are infected by carrier rodent fleas or by contact with infected animals. The flea
acquires the Y. pestis organisms during a blood meal from infected rodents. These organisms lose
their capsule (in the flea), multiply in the intestinal tract. While feeding on a human host the flea
regurgitates some of the organisms into the wound. After the incubation period of 2-7 days,
symptoms will appear.
During the incubation period the bulk of non-capsular organisms are phagocytosed and
destroyed by neutrophils. However, few organisms are taken up by monocytes that are unable to
kill them and the organisms resynthesize their capsule and multiply. The encapsulated
organisms, when released from monocytes are resistant to phagocytosis and killing by
neutrophils. The resulting infection spreads to the draining lymph nodes which become hot,
swollen, tender and hemorrhagic, giving rise to the characteristic black buboes (bubonic plague).
Inguinal, axillary, or cervical lymph nodes are the most commonly noted as grossly swollen and
sore. Septicemia (septicemic plague) will occur in 80% of the patients.
The organism spreads into the spleen, liver and lungs resulting in pneumonia. While in
circulation, the organism causes diffuse coagulation resulting in intra-vascular thrombi and
purpuric lesions all over the body. If untreated, the infection has a very high (up to 90%)
mortality. The organisms are exhaled in cough droplets, infect other humans in close proximity
and cause pneumonic plague, which is more difficult to control and has 100% mortality.
Pathogenesis: Many pathogenic factors, including exotoxins, play direct and indirect
roles in Y. pestis pathogenesis.
Yops: A group of 11 proteins, which are coded by plasmids, are essential for pathogenesis and
are responsible for cytotoxicity, inhibition of platelet aggregation, phagocyte migration and
engulfment. These proteins target dendritic cells, macrophages and neutrophils, but do not affect
T and B lymphocytes.
6

Envelope (F-1) antigen: It is a protein-polysaccharide capsule that is highly expressed at 37째C
in the mammalian host but not in the flea and is anti-phagocytic.
Plasminogen activator (fibrinolysin): Plasminogen activator (fibribnolysis) promotes the
dissemination of the organism.
Diagnosis:
Diagnosis is based on appearance of buboes. The diagnosis is confirmed by culture of a
lymph node aspirate. Extreme caution is warranted in handling of the specimen, as it is highly
infectious. Y. pestis grows well on most standard laboratory media. Fluorescent-antibody testing
is available.
Prevention and Treatment:
Hospitalization and strict isolation are the rule. Streptomycin and tetracycline are highly
effective. An effective formalin-killed vaccine is available but is recommended only for people
at a high risk. The disease is internationally quarantined and reporting of cases is mandatory.
Control of urban plague is based upon flea and rodent control.

LISTERIOSIS
Listeriosis is a nationally notifiable disease. Listeria contains 6 species only 1 of which
is a human pathogen, L. monocytogenes (human pathogen). Listeriosis is caused by the
ingestion of contaminated foods resulting in an acute febrile gastroenteritis. In pregnant
women listeriosis can result in spontaneous abortions and a mild flu-like illness. Neonatal
disease is contracted transplacentally or during delivery. Listeriosis can also cause meningitis
and sepsis in the elderly, and immunocompromised.
Morphology and Physiology:
Listeria monocytogenes is a facultative intracellular, Gram-positive coccobacillus
which often grows in short chains. The organism is motile at 250 C with a unique end-to-end
tumbling which is not seen at 370 C. The bacteria grow at 40 C and this trait is used to enrich
specimens. L. monocytogenes can also grow in high salt concentrations. The organism forms
beta hemolytic colonies on blood agar plates. Cold enrichment (storage of the sample for 24-48
hours at 40 C) is a common means select for Listeria.

7

Epidemiology and symptoms:
L. monocytogenes is a ubiquitous organism found in the soil, vegetation, water, and in the
gastrointestinal tract of animals. L monocytogenes has many opportunities to enter the foodproduction and food-processing environments. Recovery rates for the organism are common
from raw vegetables, unpasteurized milk, fresh soft cheese, and meats (including fresh-frozen
and processed chicken and beef in supermarkets and delicatessens). The major mode of
transmission is through ingestion of contaminated food and inadequately pasteurized milk (or
milk contaminated post-pasteurization). These foods include ready-to-eat delicatessen meats, hot
dogs, pate, soft cheeses, and other dairy products.
Exposure to the organism can lead to full range of diseases from asymptomatic disease,
gastroenteritis, and meningitis in healthy adults to influenza-like illness in pregnancy with
miscarriage, and neonatal disease. At greatest risk for disease are the fetus, neonates, cancer
patients and immunocompromised persons. The organisms can grow at 4ﾂｰC which means that
organism replication continues in refrigerated foods.

Listeriosis has been categorized in two forms:
1) Adult disease
2) Neonatal disease
Adult Disease:
In normal healthy adults Listeria infections are generally asymptomatic or present as a
mild flu-like illness. Some patients exhibit GI symptoms (watery diarrhea, fever, headache,
myalgias, and abdominal cramps with little vomiting) Chills and fever are due to bacteremia.
In immunosuppressed individuals, however, it can produce serious illness, leading to
meningitis. It is one of the leading causes of bacterial meningitis in patients with cancer and in
renal transplant recipients. In the elderly, the early symptoms may go unnoticed and the
infection may lead to acute manifestations of sepsis (high fever, hypo-tension). A complication
of the bacteremia is endocarditis.
Neonatal Disease:
Neonatal disease can occur in two forms: disease acquired transplacetally in utero and
disease acquired at birth or soon thereafter.
In utero acquired infection (granulomatosus infantiseptica) causes abscesses and
granulomas in multiple organs and very frequently results in abortion. This form of listeriosis
has a high mortality rate unless promptly treated.
Post窶電elivery disease has 2 presentations, early onset and late onset. Early onset occurs
within the first 5 days after exposure on vaginal delivery and is associated with sepsis and
meningitis late onset disease occurs between 5 days to 3 weeks after delivery. Late onset
presents with a purulent meningitis or meningo-encephalitis with sepsis.
Pathogenesis:
Upon infecting a cell (macrophages and parenchymal cells), the organism binds to the Ecadherin on the non-phagocytic cells via bacterial proteins (internalins). The bacteria are then
taken up into phago-lysosomes. The low pH environment activates listeriolysin O, an exotoxin,
8

and 2 phospholipase C enzymes. The bacteria are then released into the cytosol. Once in the
cytoplasm the bacteria and undergoes rapid division and become encapsulated by short actin
filaments. These filaments reorganize into a long tail extending from only one end of the
bacterium. The tail mediates movement of the organism through the cytoplasm to the cell
surface. At the cell periphery, protrusions (filopods) are formed that can penetrate neighboring
cells and allow the bacterium to move into adjacent cells. Due to this mode of cell-cell
transmission, the organisms are not exposed to the humoral anti-bacterial agents (e.g.,
complement, antibody, etc.). L. monocytogenes is readily killed by activated macrophage.
Diagnosis:
Listeriosis is indicated when blood and CSF monocytosis is observed. The organism can
be isolated on most laboratory media. Isolation of the organism from blood or spinal fluid is
diagnostic.
Treatment and control:
Penicillin (ampicillin) alone or in combination with gentamycin has been effective.
Immunity is cell-mediated.

ERYSIPELOID
Morphology and Physiology:
Erysipelothrix is a thin, pleomorphic, non-sporulating, non-motile, non-encapsulated,
microaerophillic gram-positive rod that infects through skin abrasion while handling
contaminated animal products or soil. Growth occurs on most commonly used laboratory media
(e.g., blood agar plates, chocolate agar plates). Optimal growth occurs at 30 to 37Â°C. After 24
hours at 37Â°C, colonies are small, circular, and transparent, with a smooth glistening surface and
edge. Colonies may be of two types small and smooth or large and rough, developing after one to
three days of incubation. A greening of the agar (Îą-hemolysis) under the colonies will develop
after two days. The organism is catalase and oxidase negative.
Epidemiology and symptoms:
The organism is commensal or a pathogen in a large variety of vertebrate and invertebrate
species. The major animal reservoir is domestic swine, but rodents, birds and fish are also
frequently infected. Therefore, Erysipelothrix rhusiopathiae is considered an occupational
disease with swine and fish handlers particularly at risk.
The organism gains entry into humans via scratches or puncture wounds of the skin.
Three well-defined clinical categories of human disease include: (1) a localized cutaneous form,
erysipeloid; (2) a generalized cutaneous form; and (3) a septicemic form which is often
associated with endocarditis. Erysipeloid is an inflammatory skin lesion (cellulitis), on fingers or
hand. After 2 to 7 day incubation period lesions develop which are well-defined, slightly
elevated, with a violaceous zone which spreads peripherally as discoloration in the central area
fades. The pain is severe and may be described as a burning, throbbing, or itching sensation. It
lacks suppuration and thus is distinguishable from staphylococcal erysipelas. The infection will
resolve in 3 to 4 weeks without antibiotic treatment and sooner if antibiotics are administered.
Systemic effects are uncommon.
The diffuse cutaneous form is rare. The cutaneous lesion progresses proximally
9

from the site of inoculation or appears in other areas. Blister formation may occur. The patients
often have systemic manifestations such as fever and joint pains, but blood cultures are negative.
The clinical course is more protracted, and recurrences are not uncommon. Systemic E.
rhusiopathiae infections are infrequent.
Pathogenesis:
The virulence factors include hyaluronidase and neuraminidase.
Diagnosis:
The organism can be isolated from biopsy or tissue aspirates. The organism is not
fastidious and can be grown in nutrient broth. Subculture on blood agar yields small Îą-hemolytic
colonies.
Treatment and control: Erysipeloid is easily treatable with penicillin, but inherently resistant to
vancomycin.

Bacillus
Two species of bacillus cause human disease, B. anthracis and B. cereus. These bacteria
are aerobic, Gram-positive, spore forming, rods. They are present in soil and B. cereus is
associated with the production of grains particularly rice. B. anthracis (anthrax) is considered an
organism with bioterrorism potential.
ANTHRAX
Morphology and physiology:
Bacillus anthracis is the causative agent of anthrax. It is a Gram-positive, aerobic, sporeforming bacillus. Spores are formed in culture, in the soil, and in the tissues and exudates of dead
animals, but not in the blood or internal tissues of living animals. Spores remain viable for
extremely long periods of time (up to 50 years).
Epidemiology, transmission and symptoms:
Anthrax is a disease of herbivorous animals (cattle, sheep, horses, hogs, and goats).
Humans are infected by direct contact (cutaneous) with contaminated material such as diseased
animals, or working with hides, wool, or bone meal, by inhalation (Woolsorter's disease) of
spores, or by ingestion of diseased animals. B. anthracis is not an invasive disease.
Cutaneous anthrax accounts for more than 95% of human cases. Spores enter through
breaks in the skin, germinate and rapidly proliferate at the portal of entry. Within a few days, a
small papule emerges that becomes vesicular. Rupture of this lesion will reveal a black eschar at
the base surrounded by a zone of induration but no pus or pains are associated. This lesion is
referred to as malignant pustule. The lesion is classically found on the hands, forearms, or head.
The invasion of the bloodstream will lead to systemic dissemination of bacteria.
Pulmonary anthrax results from inhalation of B. anthracis spores which are
phagocytized by the alveolar macrophages where they germinate and replicate. The organisms
released from the dying cells and infect the hilar lymph node which leads to marked hemorrhagic
necrosis. The patient may manifest fever, malaise, myalgia, and a nonproductive cough. Once in
the hilar lymph node, infection may spread into the blood stream. Respiratory distress and
10

cyanosis are manifestations of toxemia. Death results within 24 hours. This form of anthrax is of
significance in biological warfare.
Gastrointestinal anthrax: Ingestion of meat-derived from an infected animal leads to
organism proliferation within the gastrointestinal tract, invasion of the epithelium, and ulceration
of the mucosa. The organisms invade the mesenteric lymph nodes and disseminate into blood.
Initially there is vomiting and diarrhea followed by blood in the feces. The invasion of the blood
is associated with profound prostration, shock, and death. Because of strict control measures, this
form of anthrax is not seen in the U.S.
Pathogenesis:
The virulence factors of B. anthracis include exotoxins and a capsule.
Exotoxin: A plasmid-encoded, protein complex made up of 3 components: 1) Protective
Antigen (PA), 2) Edema Factor (EF) and 3) Lethal Factor (LF). In vivo, the PA combines with
EF and LF to form 2 separate toxins.
The protective antigen functions as a ligand binding to surface receptor. Anthrax toxin
receptor (ATR) is a type I membrane protein with an extracellular von Willebrand factor A
domain. Once bound the PA is cleaved into two fragments by a cellular protease. The larger
fragment then self-associates into ring-shaped heptamers. The heptamer binds up to three
molecules of EF and/or LF. The complexes are endocytosed and trafficked to endosomes. The
low pH induces conformational changes in the PA that allow it to form a membrane-spanning
pore and translocates bound EF and/or LF across the membrane into the cytosol.
Edema Factor, when inside the cells binds to calmodulin and the complex acts as
adenylate cyclase. EF causes a dramatic increase in cellular cAMP levels, upsetting water
homeostasis and destroying the balance of intracellular signaling pathways. EF is responsible for
the edema found in cutaneous anthrax.
Lethal factor is a zinc-dependent endopeptidase specific for two mitogen-activated
protein kinase kinases (MAPKKs). PA plus LF inactivates MAPKKs inducing cell death of
macrophages. Individually, the three proteins have no known toxic activity. Antibodies to
protective antigens prevent PA binding to cells and stop EF and LF entry.
Capsule: It consists of a polypeptide of D-glutamic acid that is encoded by a plasmid and is
antiphagocytic. It is not a good immunogen and even if any antibodies are produced, they are not
protective against the disease.
Diagnosis:
Clinical diagnosis of anthrax can be confirmed by direct examination or culture. Fresh
smears of vesicular fluid, fluid from under the eschar, blood, or spleen or lymph node aspirates.
Cultured organism stains as Gram-positive long thin rods.
Prevention and Treatment:
Most B. anthracis strains are sensitive to a broad range of antibiotics (Penicillin,
ciprofloxacin, or doxycycline). Quarantine is not needed. Exposure to anthrax requires antibiotic
treatment for 60 days. Currently one human vaccine is available.
11

Bacillus cereus
Morphology and physiology:
B. cereus is a close relative to B. anthracis. It is a Gram-positive, aerobic, spore-forming
bacillus found in soil. It causes food poisoning, and eye infections such as severe keratitis,
endophthalmitis, and panophthalmitis. In contrast to colonies of B. anthracis, B. cereus colonies
of are Î˛-hemolytic.
Symptoms:
Two types of food poisoning are associated with B. cereus: Emetic which causes,
nausea, vomiting, abdominal cramps. This form of food poisoning has an incubation period 1-5
hours and is self limiting with recovery within 24 hours. The second form is diarrheal with an
incubation period 1-24 hours. Diarrheal food poisoning exhibits profuse diarrhea with
abdominal pain and cramps, but fever and vomiting are uncommon.
The eye infections are generally seen after penetrating trauma. Symptoms depend on the
type of trauma.
Pathogenesis:
Three enterotoxins have been identified, hemolytic, non-hemolytic and a cytotoxin, in addition to
cereulide, a heat-stable emetic toxin.